Wikidata SPARQL, why an intermediate item is needed in this sample query?

Question

In the Wikidata SPARQL samples, I found this query:

What is the relation between Terrell Buckley and Miami Dolphins? Items used: Terrell Buckley (Q5571382), Miami Dolphins (Q223243)

SELECT ?l 
WHERE
{
    wd:Q5571382 ?p wd:Q223243 .
    ?property ?ref ?p .
    ?property a wikibase:Property .
    ?property rdfs:label ?l FILTER (lang(?l) = "en")
}
LIMIT 10

Try it

I found really hard to know why you can't simply write:

SELECT ?l 
WHERE
{
    wd:Q5571382 ?property wd:Q223243 .
    ?property a wikibase:Property .
    ?property rdfs:label ?l FILTER (lang(?l) = "en")
}
LIMIT 10

Removing the ?p intermediate variable.

The fact it doesn't work numbs me beyond comprehension, I don't know if I'm simply too stupid to understand it, but, could you help me, guys?

Answer 1

In the original query ?property and ?p are distinct values: ?property is wd:P54 (short for <http://www.wikidata.org/entity/P54>) and ?p is wdt:P54 (short for <http://www.wikidata.org/prop/direct/P54>). Notice that both refer to P54, but they are not the same. The two are connected by ?ref, which is wikibase:directClaim.

This is why your simplified query doesn't work.